Earlier quoted context omitted.
What information would your bike send to the car in this example that would help? We're closer to having lidar in all new cars than this mesh network, so "There's a bike behind you travelling approximately X speed" is something the car already knows. "The cyclist requested you not to turn in front of him" - why would anyone ever send anything else? Perhaps the car can send you a message instead "I'm going to cut you…
The idea would be more like the car, not the human behind the wheel, would realize that if it right-hooked me that would be bad (read insurance-increasing, citeable offense, etc.) and wait, where the driver would just keep flipping through their playlist and crush me.
Even if the network was there, it's a difficult physical/technological problem to figure out everyone's relative position and velocity to suitable precision with something like GPS, or GPS + accelerometers. But mostly solved with lidar.